Controlling coke in the pyrolysis of hydrocarbons to acetylene and hydrogen

ABSTRACT

A method for controlling and diminishing the formation of coke on the walls of reactors wherein hydrocarbons are undergoing pyrolysis and especially pyrolysis for formation of acetylene, which comprises injection of steam and/or an inert gas at at least one critically located point in the system downstream from the feed injection. The improvement step prolongs the period of introduction of feed to the pyrolysis by reducing the frequency of feed interruption in order to remove coke build-up.

United StatesPatent 1 1 Kramer et a1. 9

[ 1 Oct. 22, 1974 METERED METHANE/FEED 3365387 [/1968 Cahn ct a1. 208/483,487 12l 12/1969 Hallee 208/130 X 3,507 929 4/1970 Happcl ct a1. c.208/48 X 3.551.512 12/1970 Keckler et a1. .f. 260/679 PrimaryExaminer-Delbert E. Gantz Assistant Exuminer-juanita M. Nelson Attorney,Agent, or Firm-E. Janet Berry; Lawrence Roscn [57] ABSTRACT A method forcontrolling and diminishing the forma- I tion of coke on the walls ofreactors wherein hydrocarbons are undergoing pyrolysis and especiallypyrolysis for formation of acetylene, which comprises injection of steamand/or an inert gas at at least one critically located point in thesystem downstream from the feed injection. The improvement step prolongsthe period of introduction of feed to the pyrolysis by reducing thefrequency of feed interruption in order to remove coke build-up.

13 Claims, 4 Drawing Figures I I l I I l ELECTRICALLY m WINDOW HEATED 1l REACTOR l f 7 1 I g' l I 1' I QUENCHING l CHAMBER 4 SAMPLE AND PRODUCTRECYCLE BY-PAss LINE CYCLONE SEPARATOR COOLER WATER DRAIN 8 RE'CYCLEPUMP mama M122 mm 3.843.; mm SHEET 1 BF 4 fgfEYE m REACTOR WINDOW [FEEDTEMPERATURE INCREASING WW cooRs A099 H REACTOR TUBE o 3 ID. 2

MAXIMUM REACTOR w TEMPERATURE- ILLUSTRATIVE MAx ZONE OBSERVED COKINGZONE QUENCH END aawgfmm METERED CARRIER LINE HEATER VAPORIZ ER SHEET 2OF 4 )LINE METERED WATER(STEAM CONTROL VALVES HEATED REACTOR D E F E m HT E M D E R E T E M PRODUCT Qp coomz X SAMPLE AND RECYCLE BY-PASS LINESEPARATOR RECYCLE PUMP \CYC LONE QUENCHING/ CHAMBER PATENTEDHBT Z IIII3M3; WW SHEET 3 0F 4 IOI STEAM INJECTION TUBE 3/16" NOM. 0.0.

g |/4"NOM. I0. I03" REACTOR TUBE WATER COOLED H x fouTER WALL I '08 OZIRCONIA RETAINING WALL Ci I06 REFRACTORY A D ALUMINUM SILICATEINSULATION GRAPHITE HEATER ELEMENT STEAM VENT K [04 ANNULUS CONTROLLINGCOKE IN THE PYROLYSIS OF I-IYDROCARBONS TO ACETYLENE AND HYDROGEN Thisinvention relates to an improved method for controlling the formation ofcoke on the walls of reactors wherein hydrocarbon pyrolysis isconducted. In particular, this invention relates to an improvement inhigh temperature pyrolysis systems for hydrocarbons wherein the desiredproduct is acetylene, and the other principal components of the productstream are mainly hydrogen and lesser amounts of methane and ethylene.

Coke formation on the walls of hydrocarbon pyrolysis equipment isundesirable in that the coke is cumulative and eventually restricts theflow of the feed gas to such a great extent that the pyrolysis processmust be interrupted for removal of the coke. When this coke cannototherwise be controlled, it is burned-off in cycles by substituting anoxidizing gas such as air, steam, carbon dioxide or oxygen for thehydrocarbon feed. It is obviously desirable and particularly incommercial operations to extend the pyrolysis cycle as much as possible,because the coke removal cycle is a non-productive period and damagingto the reactors.

It is an object of the invention to provide an improvement inhydrocarbon pyrolysis processes for production of acetylene andhydrogen.

It is a further object of the invention to injectsteam or an inert gasat a predetermined location in the reactor to retard coke formation orremove previously formed coke.

It is another object to carry out the pyrolysis of hydrocarbons to formacetylene and hydrogen in an improved manner to minimize or avoidformation of coke.

Other and further objects will become apparent from the detaileddescription presented hereinbelow.

In comparatively low temperature processes, for instance those below1,200C., such as the pyrolysis of hydrocarbons to a desired product orproducts such as ethylene or otherhigher molecular weight olefins, it isa well-known practice to dilute the feed with steam, and in this way toretard continuously thecoke formation. An undesirable feature of thismethod of coke control is occurrence of the water-gas reaction betweenhydrocarbon and steam and which yields carbon monoxide as an undesirablebyproduct. At these low temperatures, this water-gas reaction can becontrolled so that carbon monoxide yields are minimized. However, as theoperating temperature is increased either to increase the ethylene yieldor to increase the ratio of acetylene to ethylene in the product gas,the yield of oxygenated carbon products CO and CO increases. For exampleas shown by Reid and Linden, Chemical Engineering Progress 56 47 1960),over the temperature range of 1,240C. to 1,475C. (maximum reactorprofile temperature), the combined concentrations of CO and CO producedranged from 12.5 to 239 percent of the combined concentrations ofethylene and acetylene produced. Generally, the increased production ofCO and CO follows conditions of increased severity of pyrolysis i.e.,increasing temperature and- /or increasing reaction time).

As the temperature is raised still higher to a practical level for theproduction of acetylene, i.e., 1,450C. to 2,000C. as described in U.S.Pat. Nos. 3,156,733;

3,156,734; and 3,227,771, the use of steam to control coke build-upbecomes impractical, because substantial degradation of the feed to theundesirable byproducts, CO and CO occurs with a concomitant de crease inacetylene yields. To date, no method for inhibiting these water-gas"reactions at these temperature levels has been reported.

During an experimental study of heat transfer in the pyrolysis ofhydrocarbons to acetylene, it became necessary to observe the interiorof the reaction zone; in particular, itwas considered desirable todetermine where, within the reaction zone, sufficient soot (carbon) waspresent to cloud the gas stream. To facilitate this determination, awindow was installed to permit observation of the entire reactorinterior which consisted of the inner volume of an empty 3/8 inch insidediameter (1.D.) by 8 inch long alumina tube as shown for example inFIG. 1. The remainder of the experimental system has already beendescribed for instance in Us. Pat. No. 3,156,734.

During the pyrolysis of a feed containing 34.1 mole percent methane andthe remainder hydrogen, an unusual and unexpected observation was made.When feed wasfirst admitted to the reactor, for a short time the entirereactor tube volume remained totally clear to the eye and it waspossible to look right through the reactor and into the quench zone.After a short time, as a mist or fog formed, its formation was extremely1ocalized and occurred between the point of maximum profile temperatureand the quench, nearer to the quench but within the reactor. Wlhen cokeformed, it formed in the same localized area. This coke was burned out.The experiment was repeated many times and using other feeds, alwayswith the same sequence of results as those described above. Typicalofthese experiments are the data tabulated in Table 1 below.

The feed used was 34.1 mole percent methane and the remainder hydrogenat 31.2 X 10" standard cubic feet per sec (0C, 760 mm Hgab). The maximumprofile temperature was 1,700C. to 1,725C., at We inches from quench(reactor outlet). At the start of feed flow the reactor volume appearscompletely clear and the quench appears as a dark disc at the bottom ofthe bright reactor walls.

TABLE 1 Time, Minutes from Start Pressure Drop,

Reactor clear, quench is a dark disc Mist appears inside reactor justbefore reactor exit Faint coke ridge appears on wall just before reactorexit Ridge of coke grows from wall towards center axis of reactor tube.No other coke or mist is visible at upstream locations Ridge of coke hasgrown to a plane'or sheet across reactor, obscuring quench zone, havinga pin hole for gas flow, a

second sheet of coke is growing from wall on top of first sheet Pin holein sheet closed; new hole opened Solid sheet across reactor with eithercracks or platelet edges showing zero 1 OLII Mechanical probing of thesheet indicated that it was very thin, less than one-eighth inch thick.No other coke was observable until this thin zone, located between themaximum reactor profile temperature and the quench, but much closer tothe quench, was substantially blocked. Only then did coke appearupstream and it had the appearance of water droplets on a swcating pipe.Similar results were obtained. for example, with a feed containing 25.6molc methane except that the rate of coke growth was slower.

As a result of these observations, it is clear that the pyrolysis cycle(as distinguished from the decoking or burn-out cycle) could be greatlyextended if this localized coke formation in the downstream end of thereaction zone could be controlled or retarded.

While it is not intended in any way to limit the processes or advantagesof the invention to a theory, it was found advantageous to advance somepossible reasons for this surprising, localized coke formationparticularly in order to better formulate an experimental program forits control; some but not all of the reasons proposed are included inthe following detailed listing.

The localized coke forms where:

l. The conditions for the rapid polymerization and/or decomposition ofacetylene are first encountered.

2. Free radicals, present and relatively stable at the highertemperatures of the reaction zone, first reach a temperature where theycan recombine as coke precursors and/or initiate polymerization.

3. High molecular weight species, already formed, reach a dew point.

4. Electrical forces at the interface between the reactor and the quenchzone cause agglomeration and deposition of coke precursors.

As a result of these surprising observations, it was decided to attemptto control this coke laydown by injecting a gaseous substance into theproduct stream at some point downstream of the maximum reactor profiletemperature but upstream of the point at which the localized coke forms.

In some cases, it is difficult to establish the location of the maximumof the longitudinal temperature profile of the reactor (along thedirection of flow); for example, when a relatively flat, long zonerather than a point, is found at the maximum temperature. Then, for thepurpose of the hereinafter described invention, Tmax is that location(point) in the reactor which is approximately at the maximum temperatureobserved within the reactor and which is furthest downstream (closest tothe quench). In other words, the gaseous stream would necessarily beinjected downstream of the high temperature zone of the reactor.

With respect to the hereinbefore stated proposed reasons for thisobserved localized coke formation and the possibility of injection of agaseous stream to control this coke, it became necessary to select anappropriate gas. Two readily available gaseous substances wereimmediately considered, i.e., steam and hydrogen.

Both steam and hydrogen are reactive gases at high temperatures and maybe expected to react with radicals or highly unsaturated cokeprecursors. Both gases would act to dilute the products and in this wayreduce the rates of polymerization and the dew point of coke precursors.Steam has the additional advantage that even at temperaturessubstantially below Tmax, it reacts with coke, and therefore could beexpected to reduce the net rate of coke formation still further. Bothsteam and hydrogen were also considered to be interesting from apractical point of view in that both are This, in conjunction with theparagraphs that follow should distinguish between steam and/or H in ourprocess and either or both as a quench-or diluent.

Steam has been used many times as a diluent for the feed to pyrolysissystems and also as a quenching medium injected downstream of thereactor, and in both cases it has been found ineffective in controllingcoke. When mixed with the feed, it prevents coke laydown, but, as shownabove, because of the water gas" reaction it converts much of thehydrocarbon to carbon oxides (monoxide and dioxide) rather than toacetylene and thus the yields of the desired product are poor. As aquenching medium it has no effect whatever on reactor coke formation.

However, in carrying out the process of the present invention, theinjected gas, i.e., steam and/or hydrogen, is separate from the feed andinjected, hot, into the product just before the zone of localized cokeformation described above. Since by this technique the temperature andtime for the water gas reaction are thus both minimal, the production ofcarbon oxides is greatly reduced.

In addition to controlling the formation of localized coke, a furtherbenefit results when the injected gas is heated externally from thereactor and then introduced upstream of the point of localized cokeformation; the heat load and the size of the reactor can be reduced,said reductions being impossible when steam and/or hydrogen are used asfeed diluents.

When steam was used to carry out the improvement of the invention, itwas necessary to add a relatively small amount of a non-condcnsihlc gas,such as hydrogen, to prevent hammering and condensation in the verysmall steam lines used to carry steam into the furnace. This is anadditional improvement feature of the invention.

Although coke formation is a problem encountered in the pyrolysis of allhydrocarbons to acetylene, the experimental results reported herein wereparticularly directed toward use of the improvement with methane asfeed, because the coke control process described herein applies to thatportion of the reaction zone where a substantial part of the pyrolysisprocess has been completed. Under these circumstances, the hydrocarbonspresent in the product stream are remarkably the same regardless of thehydrocarbon fed, and it is on this part of the stream, i.e., in thereactor that this carbon control process is peculiarly applicable; thesimilarity of the product stream components is illustrated below inTable 2 in order of decreasing concentration:

TABLE 2 Reference Product Feed US Patent 3,l56,733

US Patent 3,l56,734

US Patent 3,l 56,734

US Patent 3,227,77l

US Patent 3,227,77l

US Patent 3.227.77l

US Patent 3.227.77l

Hydrogen. acetylene,

methane, ethylenes Hydrogen, acetylene,

methane, ethylene Hydrogen, nitrogen, methane, acetylene, ethyleneHydrogen, acetylene,

ethylene, methane Hydrogen, acetylene,

methane, ethylene Hydrogen, acetylene.

methane, ethylene Hydrogen, acetylene,

(pure methane) (methane-hydrogen) hydrogen-methane-nitrogen methane,ethylene It is clear from the foregoing that the localized coke controlprocess described herein cannot distinguish between differenthydrocarbon fced gases which may be used, and would function similarlyin controlling the localized coke formation regardless of thehydrocarbon fed to produce the acetylene.

Besides the localized coke formation herein described, there may also beformed that type of coke which is laid down more or less uniformly andat a much lower rate over the reactor-zone walls; for this type of coke,the use of injected steam offers an additional benefit. This coke may beremoved by diverting or adding steam to the reactor inlet with orwithout shutting down the hydrocarbon feed. Obviously however if steamis added with feed flowing, the rate of coke removal will be slower andthe production of carbon oxides increased.

EXAMPLE 1 An illustrative arrangement for use in the practice of theinvention is shown in the accompanying schematic flow diagrams FIGS. 2to 4. FIG. 2 is a diagrammatic representation of the elements of anapparatus wherein the metered hydrocarbon feed in line 1 which may besuitably diluted with hydrogen if desired is passed through one or moremeter valves and then caused to pass through an electrically heatedreaction chamber 3 and is then rapidly quenched in quenching chamber 4.

. Additionally, a separate and distinct, metered steam flow which may bediluted with a non-condensible carrier gas, preferably hydrogen, isadmitted to a ceramic tube 6 passing through the same electricallyheated re action chamber. Thus, for example, the maximum temperaturewithin the reactor will be maintained in a range suitable for acetyleneproduction, e.g., l,750C. maximum profile temperature. Thehydrocarbonfeed, suitably diluted with hydrogen which is either premixed therewithor fed separately, is withdrawn from storage, metered and passed throughsuitable control valves. The pressure of the feed is measured and thisfeed stream proceeds to the electrically heated reactor 3. Similarly, ametered stream of steam and carrier is admitted to the ceramictube 11via lines 2 and 5 which tube passes through the reactor.

A suitable reactor for carrying out the herein described'process is seenin inside elevational view in FIG. 3 and in cross section in FIG. 4. Asrepresented in these drawings, which are intended to be illustrativeonly for use in practice of the invention and not in any way limitativethereof, the reactor isseen to be FIG. 4) a concentric system ofcylindrical tubes (or layers) which are progressively larger indiameter. The smallest and innermost tube 101 is ceramic and carries thesteam through the reactor to the vent point 102 where it is admixedwith, the hydrocarbon product stream which flows in the annular space104 between this innermost ceramic tube and the next size ceramic tube(i.e., the reactor tube) 103 concentric with it. The vent point isconveniently located just upstream of the point at which the sheet ofcoke forms. The ceramic steam and reactor tubes are 3/l6 inch outsidediameter (OD) (101) and 5 4 inch inside diameter (I.D.) (103)respectively and the annulus 104 positioned between the larger diameterreactor tube and the smaller diameter steam tube thus constitutes thereactor cross section of 1/32 inch nominal width. The narrow annulus 104was not chosen because its performance I i.e., operating time: Time inTable 3) is the best, but because is very sensitive to coke and thusoffers readily and quickly available comparisons of coking rates underdifferent experimental conditions. Since it is unlikely that anyproduction design would have smaller clearances, the operating timespresented in Table 3 may be considered in the minimal ranges of thosewhich would be encountered in larger reactors.

The ceramic reactor tube (alumina) is positioned within the graphiteresistance element 105 designed to use low voltage electrical power upto 3.5KVA, thus providing sufficient heat to effect the maximumtemperature within the reactor and steam tubes so described hereinabove,e.g., l,750C. the optimum temperature for production of acetylene.

Successive cylindrical walls of refractory 106 and insulation 107 arerefractory walls of zirconia 106 and aluminum silicate insulation 107within a furnace outer wall 108 of aluminum are desirably employed. Theouter walls of the reactor are preferably water cooled. A window 7 FIG.2) is positioned in the outer cylindrical wall 108 of the reactor topermit observation by an optical pyrometer sighting on the outer wall ofthe ceramic reactor tube (through slits in the insulation, refractoryand graphite resistance element); thus a means for determining thetemperature thereof is conveniently provided.

Upon leaving the annular reaction zone 104 the combined effluent streamcontaining product and byproduct, steam and carrier enters the quenchingchamher 4 where rapid cooling of the hot effluent gas to a turereduction by dilution. Additional cooling in a water cooled heatexchanger 10 for example further reduces the temperature of the effluentto ambient temperatures thus causing further condensation of the steam.Condensate and soot are desirably separated from the effluent; forinstance this can be accomplished in Cyclone separator 9. Analysis ofthe gaseous effluent components'is accomplished by gas chromotography.

It will be evident that a variety of suitable systems and reactors maybe employed for the practice of this v to a sheet form but todistinguish that coke which forms over a relatively short length of thereactor walls, grows rapidly out from the walls and forms only betweenTmax and the quench (or shock cooling) zone fromthat coke which laysdown at much lower rates both upstream and downstream of Tmax andcovering the entire reaction zone walls more or less uniformly. Althoughin the particular system described herein, the temperature of the steamat the point it is admixed with the product effluent is the same as thereaction zone temperature at this point, this is not necessarily arequirement for operation of the invention and to obtain its advantagesit is required only that the injected gas, e.g., steam, be hot, i.e.,over 750C. If steam temperature is higher than the reactor temperature,the production of carbon oxides is increased.

Furthermore, the gas, e.g., steam, for injection into the system asdescribed herein, comes in parallel, but separate from the feed. Othermeans for introducing this steam are also suitable and may be used;illustrative of but not intended to be limitative thereof, arecountercurrent injection through the reactor exit (quench zone), andalso, through a break in the reactor wall such that the gas enters thereactor perpendicular to the direction of feed flow from outside thereactor. In large and/or non-circular reactor configurations, parallelflow is the least desirable technique.

For any given reactor configuration and system, the point of secondarygas injection is best determined by experimentally conducting a shortpyrolysis cycle until the pressure drop across the reactor (inlet toquench) is about one-eighth of the pressure in the reactor. Ex-

' amination of the furnace, after shut down in an inert atmosphere(e.g., nitrogen) will show where the socalled sheet coke is forming.Secondary gas is then injected upstream of this point, desirably asclose to the point of coke formation as practically possible for thereactor system.

If it is inconvenient or impossible to open the furnace for examinationsteam injection through a movable lance can be used to determine wherecoke control is achieved within acceptable levels of carbon oxidesproduction; this will conveniently locate the point for gas injection.

EXAMPLES 2-4 The following additional examples taken from a large numberof experimental determinations are intended to be further illustrativebut not limitative of the decreased coking rate and prolonged prolysiscycle achieved by practicing the improvement of this invention.

Particularly while the hydrogen to carbon ratio of the feed gasdescribed is about 7.6 (atom H/atomC), the advantages of this inventionhave been demonstrated over a much wider range, 6 to 10.

Also, for economic reasons, it is often desirable to minimize steamconsumption (lbs. of steam/lbs. of hydrocarbon fed). The minimum amountof steam which can be used will depend upon the parameters of thereactor in which the pyrolysis is conducted parameters such as length,cross section area and shape, temperature profile, etc.; however, in thereactor design illustrated below, ratios of 0.5 and less are effective.

Table 3 shows the operating conditions and results obtained during threesets of experimental runs 2a, b, and c; 3a, b, and c; and 4a, b, and 0.At constant feed composition and relatively constant conditions oftemperature, it is clear that the following conclusions can be drawnfrom the data of these runs with regard to sheet coke control and theformation of oxygenated carbon compounds (almost entirely C0; C0production is negligible):

1. From all examples, the pyrolysis cycle with steam is substantiallylonger than the cycle with hydrogen and both are much longer than thatwith no gas injected other than the feed. Thus in Examples 2 to 4 citedherein, the pyrolysis cycle time with hydrogen injection alone isincreased over a range of 60 to 150 percent and the improvement withsteam increased over a range of 100 to 200 percent as compared to thereactor operation without the invention. All times taken are that timeto reach a pressure drop of one-half psi.

If the pyrolysis cycle is further continued to the point where thepressure drop reaches or exceeds 2.0 psi, then, as seen in Example 3, anincrease in the pyrolysis cycle time of over 100 percent is attainablewith steam as compared to no injection i.e., invention not operating).

2. The yield of CO can easily be limited to less than 5 percent of feeddisappearance where a substantial portion of feed disappearance overpercent, in all examples, has been converted to acetylene.

3. The yield of CO will increase as the point of steam injection ismovedupstream, that is, in the direction away from the quench.

In Table 4, the product analyses is shown for the total productexclusive of condensed water and carbon, and

also for that portion of the product based upon the feed- (carrierexcluded). In Table 4, the terms CO, C,,, C C Y, and Y are used andtheir meanings are defined as follows:

Co moles methane disappearing per I00 moles of methane fed per pass. I

Ca moles methane converted to C H per moles of methane fed per pass.

CE moles methane converted to C l-I per 100 moles of methane fed perpass.

Cco moles methane converted to CO per 100 moles of methane fed per pass.

YA moles methane converted to C l-l per 100 moles of methanedisappearing.

Yco moles methane converted to CO per 100 moles of methanedisappearance.

It is to be noted that the analyses presented do not include otherhydrocarbons produced and/or CO some of which appeared in all runs butonly to the extent of about 0.5 percent (mole) or less and generally.their total amount did not exceed about 1 percent; water vapor was notconsidered part of the analyses nor was nitrogen and air which did notcome through the reactor. The CO component found to be present when nosteam is used probably arises from water in the quench recycle steam,but is nevertheless included for completeness.

TABLE 3 CONDITIONS AND RESULTS OF RUNS Tmax Steam Time Gas Flow* at infrom run SCF/sec X 10 inches Pressure inches start (C, 1 atm abs) fromdrop from Example mlnzsec Feed H O carrier C quench psi** quench Sample221 4:30 17.4 29.0 9.10 1770 2 1h 1 10-3 17:00 17.4 29.0 9.10 1760 2 A 113-3 20:00 1760 2 Va 1 211 4:00 17.4 0.0 9.10 1760 Z /11 1 14-3 12:001760 2 /4 1 1 6:00 1760 Z 4; 1 2L 5:00 17.4 0.0 0.0 1760 2 V; 1 14-46:15 1760 2 4 1 311 3:00 11.10 30.0 9.10 1700 Z A 1 10-] 23130 12.7529.0 9.05 1750 2 1 13-1 24:00 A l 45:00 12.75 29.0 9.10 1750 2 1 14-147:30 2% l 31) 4:30 12.85 0 9.15 1765 2 1 10-4 7:30 0 V; l 1 1:00 0 l 363:00 12.85 0 0 1765 2 V2 1 13-4 3 :00 0 0 1 1 4:10 0 0 5 1 4L! 6:0014.39 29.5 8.65 1740 1% 1% 13-3 16:00 14 30 28.0 8.70 1760 1% 1% 14-330:00 V4 1 A 41 L45 0.0 74 l /1! 18:30 14.48 0.0 8.65 1760 1 /41 13-420:00 0.0 1% 1%: 41' 10:00 0 0 l4 1 A 12'00 14.48 0 (l 1700 1144 14-115,111 (I l) 2% 1V" Feed 5 1'4 ('H,.h'i1|nce hydrogen (nmlu'7r 1;carrier. lllll'l hyillogcn comes in with steam "Pressure drop me at is(like a measure of degree of coking Wh flow and temperature data are notshown. these data were not recorded at the specific time tnlullntcil;howcvcr data tlimcs shortly before and alter the time tabulated.indicate that these conditions did not change during the time interval.

TABLE 4.-lR()DU(. '1 GAS ANALYSIS [Mole percent] Analysis with Analysiswith carrier hydrogen carrier hydrogen included excluded based only onIced Example Sample. 11: C0 011 C2116 C 11 C 11 113 CO 011 (3 11a C211 C11 ()0 (.34: (a ((1 Ya 2th." 10-3 87. 20 0. 37 (3. 56 0. 00 0. 23 5. G581. 85 0. 52 .1. 31 0. (l0 0. 32 8. 0O 67. 55 .2. 24 55. 81 1. 80 82. 6113-3 85. 84 0. 36 7. 24 0. 00 (l. .21 5. 81. 2'.) 0. 51 10. 2'.) 0. (l00. 31 7. [i0 t'rl. .Z 11 52. 52 1. 77 81. 41)

21) 14-3 87.136 0. 23 6. 06 ll. 00 O. 23 5. 81 82. 52 0. 31. 8. 5.) U.01) 0. 33 8. .34 (31). JG .2. 313 57. 5'.) 1. 13 .3. 31 2C 14-4 84. 080. 32 5. 84 0. 01) (l. 21) J. 48 84. 01 ll. 32 5. 84 0. 00 U. 21) El. 4872!. 06 .5. 11 58. 02 1. 14 86. 03

3:1 10-1 80. 21! 0. 34 3. 00 0. O0 0. 20 5. L" 84. 11 0. (i. 38 (1.110O. 33 8.112 77. 13 1!. 35 (i1. 81 2. 01 80.18 13-1 811. 38 0. 47 4. 540. 00 U. 11) 5. 42 83. 51 0. 73 7. 05 0. 0t) 0. 30 8. 42 74. 8(1 2. 14(i0. 17 2. (i0 80. 44 14-1 88. (10 0.53 6. 82 0. [)0 0. 2O 4. 45 81. 100. 83 10. 74 U. 00 0. 32 7. 01 (i2. 83 2.111 48. 4') :2. 88 77. 18

3b 10-1 90. 58 0. 28 2. 4!) (1.00 0.111 6. 45 85. 4!) 0. 43 3. 84 0. 000. 21] 1.115 85.113 2. 14 72. 73 1. 5.) 84. 87 3c 13-4 86. 51 O. 31 3.33 0. 0O 0. 28 J. 57 86. 51 0. 31 3. 33 (l. 00 O. :38 l. 57 87. 75 2.0'.) 70. 3'2 1. 15 801 13 421 13-3 87. 31 0. 45 (i. 65 0. 00 0. 24 5. 3681. 21 0. 87 9. 88 0. 0O 0. 35 7. 93 65. 76 l. 43 55.18 2. 32 83. 0014-3 86. 0. 58 7. 03 0. 00 0. 23 5. 30 80. 43 0. 87 10. 47 0. 00 0. 347. 89 63. 67 2. 36 54. 77 3. 01 811. 02

4b 13-4 88. 77 0. 28 4. 82 0 .00 0. 24 5. J6 83. 5O 0. 2') 7. 08 0. 00O. 36 8. 77 74. J1 2. 52 62. 11 1. 04 82. 92 4c 14-4 84. 96 0. 32 5.100.90 0. 13 J. 41) 84. U6 0. 32 5. 10 0.00 O. 13 J. 4'.) 81. 56 0. 9G 68.67 1. 17 84. 20

What is claimed is: l. A process for the control of coke produced inhydrocarbon pyrolysis reactors wherein hydrocarbons undergo pyrolysis toacetylene containing pyrolysis products, by injection of a supplementarygas stream selected from the group consisting of hydrogen, steam andmixtures thereof, said gas stream being at a temperature above 750C. butlower than the temperature of the pyrolysis products at the location ofinjection into the reactor system at a location downstream from that atwhich substantially all the pyrolysis reaction has been completed butprior to the point at which the said pyrolysis products are quenched.

2. The process according to claim 1 wherein the gas injected. is steam.

3. The process according to claim 1 wherein the gas injected ishydrogen.

4. The process according to claim 1 wherein the gas injected is amixture of steam and hydrogen...

5. The process according to claim 1. wherein the gas stream is injectedat a location between that point at which the maximum reactor profiletemperature occurs and that point at which sheet coke forms underconventional operating conditions.

6. In a process for pyrolysis of hydrocarbons to acetylene, theimprovement which comprisesinjection of a 55 supplementary gas streamselected from the group consisting of hydrogen, steam, and mixturesthereof, into the reactor at a location downstream from, that at whichsubstantially all the pyrolysis reaction has been completed but prior tothe point of quenching whereby 60 production of coke is controlled andthe duration of the,

feed inlet, and is allowed to flow through the pyrolysis reactor untilcoke is removed from the entire reactor and then re-cstablishing theoriginal feed and supplementary gas stream flow pattern.

11. The process of claim wherein the feed stream to the reactor isinterrupted prior to diverting the supplementary gas stream.

12. The process of claim 7, wherein after overall reactor coking occurs,at least part of the supplementary

1. A PROCESS FOR THE CONTROL OF COKE PRODUCED IN HYDROCARBON PYROLYSISREACTORS WHEREIN HYDROCARBONS UNDERGO PYROLYSIS TO ACETYLENE CONTAININGPYROLYSIS PRODUCTS, BY INJECTION OF A SUPPLEMENTARY GAS STREAM SELECTEDFROM THE GROUP CONSISTING OF HYDROGEN, STEAM AND MIXTURES THEREOF, SAIDGAS STREAM BEING AT A TEMPERATURE ABOVE 750*C. BUT LOWER THAN THETEMPERATURE OF THE PYROLYSIS PRODUCTS AT THE LOCATION OF INJECTION INTOTHE REACTOR SYSTEM AT A LOCATION DOWNSTREAM FROM THAT AT WHICHSUBSTANTIALLY ALL THE PYROLYSIS REACTION HAS BEEN COMPLETED BUT PRIOR TOTHE POINT AT WHICH THE SAID PYROLYSIS PRODUCTS ARE QUENCHED.
 2. Theprocess according to claim 1 wherein the gas injected is steam.
 3. Theprocess according to claim 1 wherein the gas injected is hydrogen. 4.The process according to claim 1 wherein the gas injected is a mixtureof steam and hydrogen.
 5. The process according to claim 1 wherein thegas stream is injected at a location between that point at which themaximum reactor profile temperature occurs and that point at which''''sheet coke'''' forms under conventional operating conditions.
 6. Ina process for pyrolysis of hydrocarbons to acetylene, the improvementwhich comprises injection of a supplementary gas stream selected fromthe group consisting of hydrogen, steam, and mixtures thereof, into thereactor at a location downstrEam from that at which substantially allthe pyrolysis reaction has been completed but prior to the point ofquenching whereby production of coke is controlled and the duration ofthe pyrolysis cycle is increased.
 7. The improvement of claim 6 in whichthe supplementary stream is steam.
 8. The improvement of claim 6 inwhich the supplementary stream is hydrogen.
 9. The improvement of claim6 in which the supplementary stream is a mixture of steam and hydrogen.10. The process of claim 1 wherein after overall reactor coking occurs,at least a portion of the said supplementary gas stream is diverted tothe pyrolysis reactor feed inlet, and is allowed to flow through thepyrolysis reactor until coke is removed from the entire reactor and thenre-establishing the original feed and supplementary gas stream flowpattern.
 11. The process of claim 10 wherein the feed stream to thereactor is interrupted prior to diverting the supplementary gas stream.12. The process of claim 7, wherein after overall reactor coking occurs,at least part of the supplementary gas stream is diverted to the reactorinlet, and is allowed to flow until coke is removed from the entirereactor followed by re-establishment of the original feed flow pattern.13. The process of claim 12 wherein the feed stream to the reactor isinterrupted prior to diverting the supplementary gas stream.